Inverse time-limit relay



Dec. 7, 1926. 1,609,770

w. H. PETERSEN INVERSE TIME LIMIT RELAY Filed May 26. 1921 FIG. 1.

Fie.2.

. L i X h N i 9 P Patented Dec. 7,

- UNITED s'ra ES PATENT OFFICE. I

SVENSKA ELEK TRISKA. 0F SWEDEN.

AKTIEBQLAGET, OF VASTERAS, SWEDEN, A CORPORATION INVERSE TIME-LIMIT RELAY.

Application filed Kay 26, 1921, serial No. 472,848, and in Sweden October 7, 1926.

Relays of the inverse time limit type (that is relays where the time for releasing varies inversely as the operating current), as hitherto constructed, generally present certain disadvantages which prevent a satisfactory protecting action. I r

The most usual fault is probably the socalled creeping that is the timing mechanism of the relay beginning to move at a lower current value than that for which the relay is really intended to operate. If the current has, for a comparatively long time, been just a little below the operating value and then rises to or above this value, it may thus happen that the releasing is effected in much shorter time than is really intended.

Another fault, which is particularly frequent in solenoid relays, is that the return to the initial position ii the overload disappears before the releasing has occurred, is not effected untilthe current has dropped considerably below the value for which the relay started. Further the shape of the timing curve is often inapproprlate, so that, for instance, thedifference between the maximum releasing time-at the current value for which the relay is set-and the minimum time-at the highest possible current is too large. If the relay is for instance set for seconds releasing time at a certain overload currentthe smallest. value for which it releases-with many relays, at 4 to 5 times this current, the time drops to about two, or three, seconds and remains then constant at this value-the so-ca'lled shortcircuit timefor any further increase in the currentvalue until complete short circuiting of the line. Therefore if short-circuit occurs, there is nothing ensuring that differently timed relays perform their releasing action in the proper order.

The resent invention relates to an in-q verse time limit relay of induction type which is free from the aforesaid disadvantages. The creeping is avoided by an arrangement such that the releasing mechanism is normally 'free from the operative device and is automatically connected thereto just when the latter, in moving, begins to develop its full torque (corresponding to the with a speed proportionalto the releasing current value). By the same arrangement the return movement is also facilitated, because the coupling is released as soon as the torque drops below the aforesaid value. Since no constant torque counteracting that of the current is needed for preyenting the creeping, the speed of the drivmg device can be made-any desired function of the operating current, whereby the shape of the time curve can be varied within wide llrnits. The ratio of normal releasing time to short-circuit time can therefore be varied at will down to 1:1.

The couplingof the driving device to the releasing mechanism can be BEBCtQdyfOI' instance, by means of a special magnet which is adjusted to act for a certain amount of current. The arrangement is, however, simplified, and the adjustment for different-current values facilitated, if the torque acting upon the driving device be utilized for the coupling movement, the arrangement being such that the driving device is supported by a member capable of being swung into en gagement position by a direct action of the .said torque.

A construction, according to the inventlon, based upon the lastsmentioned principle is shown in the accompanying drawing in siderelevation in Fig. 1 and in plan in Fig 2.

Til he induction disc at, as usual, rotates between the poles of a driving electro-magnet f and between those of a braking magnet g torque exerted by the first named magnet, which torque may, in its turn, be proportional to the exciting current. Inhitherto known constructions of similar kind, the rotation of the induction disc has been counteracted by a weight, or a spring, or the like which has prevented said-rotation until the torque has exceeded a certain value. According to the present invention, no such counteracting member is used, and the disc a can start rotating as soon as the induced torque exceeds the friction at rest'which can be reduced to a very 'lowvalue by roviding the disc with conical pivots. e releasing mechanism, on the contrary, is not normally moved, since it is not coupled to the driving device. In the form shown, the transmission of the movement from the latter to the former is effected by a worm, h engaging a toothed segment 71. When the latter has been moved through a certain angle, it presses a movable contact piece It against a fixed contact piece Z.

The engagement between the worm h and the segment 2 is, in the example illustrated, effected in the following manner. The shaft p, carrying the disc 0', and the worm h, is journalled in a rocking frame I), fulcrumed on a shaft 0 parallel to the shaft p. The frame is balanced by a counterweight n which also by reason of its position between two stops d serves to the said frame. By means of an adjustable spring e, the frame I) is normally held in such a position, that the worm h is not in engagement with the segment a. Assuming disc a ,to rotate inan anti-clockwise direction in Fig. 1, the magnetic forces acting upon it, which practically counterbalance each other with respect to the shaft 17, exact a resultant torque in anti-clockwise direction about the shaft 0- which is situated at some distance from the shaft p. As soon as the current and, consequently, the torque have reached a certain value, the right hand .end of the frame I) is therefore raised so as to bring the worm h into-engagement with the segment 2'. After a certain time, depending upon the current value, the segment forces the contact pieces k and Z into contact with each other. Should the current, before that time, drop below the value for which the apparatus has been set, the engagement between the worm k and segment i is at once released whereupon the latter is returned to its initial position, which may be done, for instance, by means of a-spring (not shown). For facilitating the releasing of the engagement between worm and segment, the motion of thefform'er at releasing should be in a direction at an angle to the longitudinal direction of the teeth. The axis 0 should therefore have an eccentric osition ,relatively to the centreplane of t 1e segment.

The setting of the ap aratus for different time limits is preferably effected by means of a screw m which defines the initial position of the segment. The setting for .different current values may be effected in any known, or suitable, manner, for instance by connecting a greater or smaller portion of the coil o In the circuit, the said coil" for this reason being shown with a lurality of taps. The critical current value or which the releasing mechanism begins to operate is in this manner automatically regulated, the engagement ofthe mechanism being dependent v of the torque acting upon the operating de vice.

The feature of a permanently rotating oplimit the movements of crating devicedisc a and-worm kinvolves also an increased safety for the function of the relay in the event of an overload. When the engagement is effected, the segment 2' 15 immediately acted upon by a strong torque,

especially on account stored in the disc a. Even if the segment should present a comparatively large initial friction, due to an extended period of inactivity, there is thus no danger that it will not be started at once. v

Having now particularly described the nature of my said invention and the manner of its operation, I declare that what I claim is:

1. In inverse time limit relays, an electrd magnet, an'operating device kept in rotation around an axis under the influence of induction forces from said electromagnet and braking forces normally counterbalancin these, said operating device being capable o a swinging movement under a couple of forces formed by said induction and said braking forces.

2. In inverse time limit relays, an electromagnet, an operating device kept in rotation by induction from said electromagnet, a rocking frame supporting said operating device, and' a releasing mechanism capable of beingengaged by said operating device by rocking said frame.

3. Ii inverse time limit relays, an electromagnet, an operating device kept in rotation by "reduction from said electromagnet, a braking device for said operating device, aframe supporting said operating device and capable, of rocking-about an axis parallel to the axis of rotation of said operating device, and a releasin mechanism capable of being engaged by said operating device by-rocking said frame.

4. In inverse time limit rela s, an electromagnet, an induction disc capa le of rotation under the influence of said electromagnet, a

of thekinetic energy worm connected to said disc, a rocking frame supporting said disc and worm, a pair of contacts, and a toothed segment capable of being engaged by said worm by rocking said frame foractuating said contacts. 5. In inverse time limit relays, an electromagnet, an induction disc capable of rotation, under the influence of said electromagnet, a worm connected to and rotating with said disc, a frame supporting said disc and worm and capable of rocking about an axis parallel to the 'axis of rotation of said disc and worm, a toothed segment capable of being en aged by said worm and having its center p ane eccentric with Ms ect to the rocking axis of said frame, an a pair of contacts capable of being actuated by said toothed segment.

6. In inverse time limit relays, an electro- .magnet, an induction disc capable of rotation under the, influence of said electromagnet, a worm connected to said disc a toothed segment, a frame supporting said tion member, electroma etie means for rodisc and WOIIH and capable of being rocked tating said member, an a counter-balanced so as to bring said worm into engagement rocking frame sup orting said member. 16 with said segment, contacts actuated by said \In testimony W ereof I have signed my 5 segment, and means for adjusting the initial name to this specification.

position of said segment.-

7. In induction relays, a rotatable induc- WILHELM HENNING PETERSEN, 

